In recent years digital technique has been widely used in electronic devices such as audio equipment as well as video equipment, so that the speakers to be used in these electronic devices are strongly required to have a better performance. The performance of a diaphragm of speakers is a crucial factor to determine the sound quality. It is thus an urgent need to develop a high-performance diaphragm that can achieve a better sound quality.
In the audio equipment industry or the automobile industry that uses audio equipment in automobiles, the sound quality of speakers has been dramatically improved according to the spread of digital devices. In these industries, speakers trend toward quality sound, light-weight, and environmentally friend. To pursue the quality sound, it is crucial to develop a diaphragm that satisfies users' acoustical need.
The diaphragm development has been focused on paper diaphragm, e.g. Patent Literature 1, because the paper diaphragm allows advantageously a more accurate control over the sound quality. Wood-pulp is used as the material for the paper diaphragm, and among the wood-pulp, craft pulp obtained by beating conifers is used. However, a shortage of the conifer has been accelerated by the extravagant use, so that used of an environmentally friend material is essential in the future.
The paper diaphragms many of which are formed of craft paper made from conifer have generally a lower rigidity than diaphragm formed of metal material or resin material. It is thus difficult for the paper diaphragm to improve the rigidity from the material view of point. The speaker employing the paper diaphragm is thus disadvantaged in clearer sound reproduction that is one of the factors in quality sound, as well as in larger output and in higher reliability.